Production of organic acids by the alkaline fusion of cellulosic materials



` .Allg 28, 1934- w. J. BANNlsTl-:R 1,972,059

PRODUCTION OF ORGANIC ACIDS BY THE ALKALINE FUSION OF CELLULOSICMATERIALS Filed Feb. 28, 1929 2 Sheets-Sheet l Z6 Z0 Q "5 o Z606' s I 2Sheets-Sheet 2 W. J. BANNISTER Filed Feb. 28, 1929 Aug. 28, 1934.

PRODUCTION OF ORGANIC AoIDs BY THEALKALINR FUSION OF cELLULOsIcMATERIALS WHAM J. Btnnisnr- 6PM' 1. QWATTORNEYS.

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Patented Aug. 28, 1934 UNITED STATES PATENT OFFICE TERIALS FUSION OFCELLULOSIC MA- wiuiam J. Bannister, Terre Haute, 1nd., signor toCommercial Solvents Corporation, Terre Haute, Ind., a corporation ofMaryland Application February 28, 1929, Serial No. 343,402 5 Claims.(Cl. 260-119) The present invention relates to a method for theproduction of organic acids from cellulosic materials, and moreparticularly to the production of acetic acid'from cellulosic materialssuch to reduce the cost of producing the oxalic acid and no methods ofobtaining optimum yields of the former were described. The production oforganic acids other than acetic and oxalic was not reported by theseinvestigators, nor has any other investigator disclosed a processwhereby acids such as acetic, oxalic, formic, succinic, etc. can beobtained by the alkaline fusion of cellulosic materials.

The method recommended by previous workers for the production of oxalicacid by the alkaline fusion of corncobs consisted of treating groundcorncobs with two and one-half times their weight of caustic soda in asuitable vessel. A small amount of water was added and the mixturestirred and heated. Heat was controlled very carefully to avoid charringand the temperature brought very slowly up to 200 C. When the massturned a lemon yellow color, the The mass was then lixviated by acounter-current method for the recovery of the products formed. Thetreatment from this point on was to fractionally crystallize the oxalateand acetate of sodium, remove the oxalate and treat with lime to obtainthe original sodium hydroxide and calcium oxalate. This calcium oxalatewas then treated with sulphuric acid to obtain pure oxalic acid.

By carrying out the alkaline fusion of corncobs and other cellulosicmaterials according to the method hereinafter described, difficultiesexperienced by previous investigators are largely overcome, and at thesame time it is possible to obtain larger yields of total acids andlarger yields of acids of greater value and of much wider commercialapplication than formerly. Previous investigators, who have generallybeen interested in obtaining maximum yields of oxalic acid, haveexperienced considerable diiculty due to the charring of the cellulosicmaterial at the temperatures required by the reaction. Another distinctdisadvantage of such processes has been the large excess of alkali whichit was found necessary to employ. These disadvantages are largelyovercome in my improved process. In addition, the yields of aceticacid-a lproduct of considerably greater commercial importance thanoxalic acid-are much higher, and at the same time considerablequantities of oxalic,.formic and succinic acids are obtained. Smallquantities- 1% or less-of higher acids such as butyric, propionic, etc.,are also produced. v

I have discovered that improved yields of acids and especially of aceticacid may be obtained by making use of somewhat higher temperatures thanrecommended by previous investigators, by increasing the length of timerequired for the reaction, by carrying out the fusion under pressure,and by decreasing the ratio of caustic to cob, previous recommendationsbeing that a much greater caustic to cob ratio must bc used in order toobtain maximum yields. My process consists essentially of fusing cobmeal or other suitable forms of cellulosic material with the requiredamount of caustic soda and small amounts of water. In carrying out thefusion it has been found that best results are obtained if thetemperature of the mixture is quickly raised to the reaction point(160-280 C.) and then held at this point for a predetermined time. Theheating is carried out in a closed vessel and under pressure, thusavoiding danger of too rapid dehydration of the chargeand spontaneousignition. A gas formed as a reaction product,'and consisting largely ofhydrogen, is permitted to escape through a safety valve or pressureregulator, set to hold the pressure at any desired point. At theconclusion of the reaction, the melt is treated for the recovery of theorganic acids which are present in the form of their sodium salts. Oneof the distinct advantages of my process enters into play at this pointsince other investigators have frequently encountered didiculty inltering the melt due to the presence of colloidal material. Little or nodiiculty is experienced in this respect when conducting the fusionaccording to the method which I have specied.

As has been previously indicated, I have found that the production ofthe maximum yields of acids depends at least in parton the ratio ofcaustic to cob, the ratio of water to caustic, the temperature, and theduration of the reaction. The ratio of the particular acids formedappears also to be dependent at least in part on the ratio of caustic tocob and the temperature of reaction. By the term ratio of caustic to cobis meant the relative amount in parts by weight of caustic and ccbemployed. For example, the ratio 0.6 means that caustic and cob werepresent in the ratio of six parts by weight of caustic to ten parts byweight of cob. The term ratio of water to caustic is similarly employed.In

the discussion of results which follows, the time f' of reactionexpressed is the length of time which the charge is held at the reactingtemperature after having been brought up to that temperature.

As the result of an extensive series of experiments in which the factorsmentioned above have been varied over a fairly wide range, it has beenfound that altho both the total yields of acids and the relativeproportions of these acids may be changed, variations of the latter typeare probably the more marked. In the case of acetic acid, I have foundthat with a caustic to cob ratio of 0.6, the yield is independent of thetemperature and reaction time within the limits of 200 and 260 C. and 2to 8 hours. However, as shown in Figure I, for a given period oi' timethe effect on yield of changing the caustic to cob ratio varies with thetemperature. At 200 C. the yield of acetic acid grows as the ratio ofcaustic to cob is increased between 0.6 and 3.0; at 240 C. the yieldreaches a maximum at the caustic to cob ratio 1.8 and falls 'oil as thelatter is further increased, and at 260 C. the maximum yield is obtainedat a ratio of caustic to cob of about 1.0.

As stated above, the time factor has little or no iniiuence on the acidyield at a caustic to cob ratio of 0.6. On the other hand, at higherratiosI (see Figure II) the yields for the 2 and 8 hour runs arehighest, the yield for the 4 hour run is lowest and that for the 6 hourrun is intermediate.

Runs were also made at a time of eleven and one-half hours. In thisinstance, the temperature was slowly raised to 240 C. in the course ofnine and one-half hours, instead of the usual one hour, and thenmaintained there for two hours. The yields rose sharply to a maximum atthe caustic to cob ratio of 0.8, and then fell abruptly.

Generalizations for the yields of formic acid cannot be made, as in nocase do the yields follow any orderly course, very wide and sharpvariations occurring under each of the conditions discussed above.Apparently these variations in yields are due to the fact that formicacid is converted to oxalic acid with the liberation of hydrogen, andvarious factors cause this reaction to take place in some cases morethan in others. Best yields were obtained at 200 C. and two hours timewith caustic to cob ratios of 0.8, 2.0 and 3.0; at 200 C. and six hourstime a ratio of 1.0 gave optimum results; at 240 and-two hours time aratio of 0.9 was found most desirable; with the temperature remaining at240 C. and the time increased to four or six hours,

the optimum ratio was found to be 1.3; yat the slow heating at 240 C.during the eleven and one-half hour intervals, the optimum caustic tocob ratio was found to be 0.9. These represent the best yield pointsobtained. In general, however, the yield of formic acid diminishes asthe concentration of caustic soda becomes greater, as the duration ofthe run becomes longer, and as the temperature of the reactionincreases.

Also, no generalizations` c!!! ik im* la' lthe oxalic acid yields. Goodlwane obtained with a caustic to cob ratio of.' amiiamoperatfngtemperature of 200 C. u iinrlvllours time; with a ratio of 2.0 mitm*.Mladic of 0.9 at 260 C., the reactioni in each of the latter cases..Albwylboniic acid was accompanied by' with d oxalic acid and vice versa,for thev Jv- -M.

It is likewise difcult to M that will hold under all conditions ww theamount of succinic acid p Ae a rule, however, it may be stated Mmproportion of acetic and formic acidkilmu o! the succinic acid will below andi mm In carrying out my processiltwwfmd that some water must bepresent. andstocaustic ratio of 0.2 to 0.6 was found www resuits. Whilethe function of? W M i not definitely known there are sonw that itreacts with the succinic acidi @bythe following equation:

'I'his would explain why the yieldlof acid is high when that of succinicacidislbw, and vice versa.

As will be readily seen from the? Jdis cussion, the relativeproportionsi ot tits various 1m products formed may be varihd bly simplyby varying one or mow of this operating conditions. In general,howeiun,7 unibas these factors are changed so as to remmimwpreciablyfrom the optimum operaiim comme. the l total yields of organic acidswillililiii'rlvckmstant for diii'erent operating conditions; ami mly therelative proportions of the severalihdlbiilal acids will be materiallychanged. A typicalylclrl based on the weight of corncobs containing'11%'1of mois- 115 ture is as follows:

Per cent Acetic acid 25 Oxalic arid 30 Formic acid 15 m Succinic acid 10These yields were obtained by out the fusion with caustic soda in aclosedi container at approximately 'I5 pounds per squarev inch pressure,using a caustic to cob ratio 1*.0. aiwater to 125 caustic ratio of 0.2,a temperature'of. 26`0`PC. and a two hour period of reaction. By toFigure I it will be seen that these conditions represent approximatelythe optimum' conditionsfor the formation of acetic acid for a 2 hourfusion. As illustrated by the results shown above, it has been observedthat the acetic acid produced under any particular set of conditionsusually amounts to about one-half the sum of the oxalic and formicacids.

'I'he mechanism of the reactions involved in the alkaline fusion ofcellulosic materials such as corncobs is of such a character that fewstatements of a conclusive nature can be madeconcerning it.

It appears to me, however, that the rst reaction taking place is thehydrolysis of the acetyl group of the non-cellulosic part of thecorncob. `This takes place if only water or alcohol is used with nocaustic present, and amounts to a yield of acetic acid equivalent toabout 5% of the cob. y

The next reaction seems to be a breaking down of the cellulose moleculeby the sodium hydroxide under the conditions employed, with the probableformation of the sodium salt of a complex intermediate acid in additionto me sodium sans or acetic and formic acids. The formation anddecomposition to sodium succinate and then to sodium acetate and formateof the intermediate compound would naturally be greatly affected bycaustic concentration, temperature and time of reaction, and hence it isnot surprising that these factors have a decided influence on the natureand yield of the iinal products.

It is believed that most of the oxalic acid produced in the reaction isnot formed as a direct product of the decomposition of cellulose, butowes its origin to the decompostiion of formic acid:

COOH 00H The decomposition of the intermediate acid would constantlyfree new formic acid, a part of which may be decomposed sooner or laterto oxalic acid. Thus, the irregularity of the yield of formic acid isexplained, as is also the fact that in general the yield of formic acidis higher in runs at lower temperatures and at lower sodium hydroxideconcentrations.

The above discussion gives a satisfactory working explanation, but itwill be understood that it is not desired nor intended that it beconstrued as, nor limited in meaning to, the exact mechanism of thereaction involved in this present process.

The results obtained in numerous experiments indicate that the fusionsshould be conducted with low concentrations of caustic soda at a fairlyhigh temperature and for a short period of time. The conditions mostfavorable for good yields are the following, it being understood thatrelatively slight variations therefrom are permissible. c

Ratio of water to caustic 0.2-0.6

2HCOOH- -i-HI Ratio of caustic to cob 0.9-1.2 Temperature 255265 C. Time1-3 hours Sodium hydroxide has been found to give better results in thefusion than any other of the common alkaline materials. The addition ofother alkaline compounds or of auxilary inorganic oxidizing materialsdoes not increase yields of the organic acids.

The yield of acetic acid is increased as the temperature is raised up toa certain limit. This limit rises as the sodium hydroxide concentrationdecreases.

In general, better results are obtained in short fusions than in longones, but if the time of fusion is increased considerably, good yieldsof acetic acid are again obtained.

The cob meal need not be very fine, as fairly coarse material of about 5to 8 mesh, gives equally good results.

Pressure is necessary for good results. However, 50 or 'I5 poundspressure gives as good results as much higher pressures. 'Ihe solefunction of pressure in this instance seems to be to prevent too rapiddehydration of the cobs. Open pot fusions not only give poorer yields,but are extremely hazardous, due to the tendency for spontaneousignition to occur.

In the data given in Figures I and Il, 'the yield figures refer to thenumber of grams of anhydrous acids resulting from grams of cob (moisturecontent '7 charged. The sodium hydroxide used was about 93-95% NaOH, therest being sodium carbonate and water.

The products of the fusion may be recovered by any of the known meansfor separating formic,

acetic, oxalic and succinic acids from mixtures containing these acids.

The above description shows the procedure which I prefer to follow.Results were, however, also obtained by the use of the following commonalkaline materials other than caustic soda, although the yields weresmall: lime, barium hydroxide, potassium hydroxide, lithium hydroxide,ammonium hydroxide, and mixtures of sodium and potassium hydroxides.Inthe last mentioned instance, the caustic potash did not increase theyields materially, and in the remaining instances, the yields obtainedwere always lower than when caustic soda was employed.

Also, there was substituted for the cobs, cellulosic materials otherthan that described above. For example, oat hulls, cotton waste, andfermented residue from the Langwell cellulose fermentation process, etc.were employed. 'Ihe fermentation residues gave good yields, but in othercases the yields were low. All of these substitutions, however, fallwithin the concept of the present invention, and it will be understoodthat it 1s desired to include within the scope of this invention suchmodifications and changes as may be necessary to adapt it to varyingconditions and uses.

As previously pointed out, the presence of liquids such as water,alcohol and the like are necessary for the production of eflicientyields. The function of these compounds, however, is not clearlyunderstood since it appears that their action is upon the cellulose aswell as the noncellulose ingredients of the cob or other material beingemployed. These liquids may be omitted altogether, and the reaction willproceed, but it may be pointed out that a certain amount of water willbe produced as one of the products of the reaction, so that some eifectof water will be manifest even if the water be originally absent fromthe mixture as formed. However, as previously mentioned, the presence ofliquid in the aforesaid ratios is necessary for efficient results, andVone of the effects of such liquid is probably the hydrolysis ofamylaceous portions of the cob. Therefore, the liquids employed aredefined in the claims by the term hydrolyzing liquids, or equivalentexpression but it will -be understood that this expression is notintended as a limit of the function of these liquids since their actionis in fact not clear, and may be even largely of a physical rather thanof a chemical nature.

Now having described my invention, what I claim is:

1. In a process for the production of organic acids of the groupconsisting of acetic, formic, oxalic and succinic acids fromcellulose-containing material, the improvement which comprises fusingsaid material with caustic soda at temperatures from 20G-260 C. andunder a pressure 135 in excess of 50 lbs. per sq. in.

2. In a. process for the production of acetic, formic, oxalic andsuccinic acids from cellulosecontaining material, the improvement whichcomprises fusing said material with caustic soda in a ratio of causticsoda to cellulose-containing material ranging from 0.9 to 3.0, attemperatures from 20D-260 C. and under a pressure in excess of 50 lbs.per sq. in.

3. In a process for the production of acetic, formic, oxalic andsuccinic acids from cellulosecontaining material, the improvement whichcomprises fusing said material with caustic soda at temperatures from20G-260 C. and in an atmosphere comprising the gaseous reaction prod-.ucts oi.' the fusion maintained under a pressure in excess of 50 lbs.per sq. in.

4. In a process for the manufacture oi' acetic, formic, oxalic andsuccinic acids from cellulosic materials, the improvement whichcomprises forming a mixture oi' caustic soda, cellulosic material andwater in the ratio ranges of water to caustic soda of 0.2 to 0.8 andcaustic to celiulosic material of 0.9 to 3.0, and rapidly heating saidmixture in a closed container to a temperature range of 200 C. to 270C., and maintaining said temperature for a period of one to three hours,and under a pressure in excess of 50 pounds per square inch.

5. In a process for the' production o! acetic, i'ormic, oxalic andsuccinic acids from celiulosic materials, the improvement whichcomprises forming a mixture of caustic soda, ceilulosc material andwater in the ratio rang of water to caustic soda oi.' 0.2 to 0.0. andcaustic to cellulosic material of 0.9 to 1.2, and heating said mixturein a closed container to a temperature range of 240 C. to 270 C., andmaintaining said temperature i'or a period of one to three hours, andunder a pressure in excess oi 50 pounds per square inch.

WILLIAM J. BANNISTER.

